MetroWest Water Supply Tunnel (604) Project Purpose and Benefits 6 Contributes to improved public health 6 Fulfills a regulatory requirement 6 Extends current asset life 6 Improves system operability and reliability To provide transmission redundancy for the Hultman Aqueduct ensuring reliable water delivery and providing sufficient hydraulic capacity to support the new Walnut Hill Water Treatment Plant and covered storage distribution facilities. This project consists of construction of a 17.6 mile deep rock tunnel from Shaft D in Marlborough to Shaft 5 of the City Tunnel in Weston, and to Shaft W, also in Weston, as well as the construction of a covered storage facility at Loring Road in Weston. Also includes construction of shafts and valve chambers for connections of Shaft 4 in Southborough and to the Norumbega Covered Storage facility. Project History and Background Provision of adequate transmission capacity is a critical component of MWRA’s Integrated Water Supply Improvement Program. MWRA's water delivery depends on a system of tunnels and aqueducts that transport water from the Quabbin and Wachusett Reservoirs to the distribution reservoirs in western metropolitan Boston. The existing tunnels and aqueducts are deficient in several respects. First, the transmission system is unable to supply sufficient hydraulic capacity during peak flow periods, leading to pressure deficiencies in all high service areas during the summer months. Second, key sections of the transmission system, such as the Hultman Aqueduct and the Southborough Tunnel, rely on a single conduit. In the event of failure of any of the major transmission sections, the remaining waterworks system could not meet the demand for water. Construction of the MetroWest Water Supply Tunnel and its extension to the Weston Aqueduct Terminal Chamber will provide the critically needed minimum level of transmission redundancy for the Hultman Aqueduct. In the future, enhancements and improvements to the reliability of the City Tunnel and the City Tunnel Extension will be planned as part of the Metropolitan Tunnel Loop project. This will also enhance system maintenance by allowing each major supply conduit to be taken out of service for inspection, cleaning, and repair. In June 1989, MWRA began engineering work on reconstruction of the Sudbury Aqueduct. On May 9, 1990, the Board of Directors directed staff to put minimum effort into further study of the Sudbury Aqueduct reconstruction alternatives and maximum effort into study of the all-tunnel alternative. The advantages of tunneling included a large reduction in surface activities resulting in a reduced environmental impact, and the potential to obtain a large increase in water transmission capacity to enable the tunnel to supplant the Weston Aqueduct as well as provide redundancy to the Hultman Aqueduct. Other advantages included a higher pressure rating by constructing a tunnel deeper into rock, and the ability to construct along a straight line, reducing the overall length of the project by three miles. In November 1990, the Board of Directors directed staff to eliminate the planned tunnel from Norumbega Reservoir to the Chestnut Hill Reservoir in favor of connecting to Shaft 5 of the City Tunnel and to the eastern end of the Weston Aqueduct. The connection will allow the Weston Aqueduct and Weston Reservoir to be taken off-line and used only for emergency supply as required by the Safe Drinking Water Act. In December 1995, the Board of Director’s approved staff’s request to solicit bids on the first major construction contract of the MetroWest Tunnel project. In June 1996, a notice to proceed was issued on this contract, beginning the transition from design to construction of the project. Program Elements When completed, the MetroWest Tunnel will be 17.6 miles long with a 14-feet finished diameter. The first segment of the tunnel extends from the water treatment plant site at Walnut Hill on the Marlborough/Southborough line to Shaft 4 of the Hultman Aqueduct in Southborough. From there, the tunnel continues to a "WYE" connection east of Norumbega Reservoir, and continues east from the "WYE" to Shaft 5 of the City Tunnel and northward to the Weston Aqueduct Terminal Chamber. The tunnel depth varies from 200 to 500 feet below ground surface along the alignment. Following start-up of the MetroWest Tunnel, the Hultman Aqueduct will be inspected and rehabilitated. Surface distribution facilities, including piping, valve chambers, and risers will connect the tunnel to the Hultman Aqueduct and local community services. Intermediate connections between the MetroWest Tunnel and the Hultman Aqueduct Transmission 101 will permit operation of segments of either the aqueduct or the tunnel interchangeably, allowing flexibility in the maintenance of the two conduits. Scope Sub-phase Scope Study Study of the aqueduct/tunnel system to determine the best alternative to improve hydraulic capacity and create redundancy. Construction- Rehabilitation of the Siphon Pipe Bridge at the Weston Aqueduct which Sudbury Pipe experienced significant leakage. Bridge Design/EIR- Environmental impact report (EIR) process and design of the 17.5-mile long, 14- Tunnel- feet diameter tunnel. Construction support services, including environmental and Engineering safety compliance, claims assistance, contract administration, quality assurance Services During testing, and community relations. Construction (ESDC) Construction: Construction of the western portion of the tunnel and associated surface facilities. Western Tunnel Shaft E was constructed at the Sudbury Dam and a tunnel has been excavated 4.9 Segment – CP1 miles to Shaft D, located adjacent to the clear well of the Walnut Hill Water Treatment Plant (WHWTP). A riser shaft has been excavated to connect the tunnel to Southborough's Hosmer Pump Station and includes the surface piping facilities necessary to bring water from Wachusett. Construction: Construction of approximately 11.9 miles of tunnel between Southborough and Middle Tunnel Weston. Construction is staged from Shaft L, located at a sand and gravel pit in Segment – CP2 Framingham, where a permanent connection to the Hultman will be constructed. Along the alignment, four small-diameter shafts will be constructed for community connections to Framingham and Weston. The western reach of the Middle Tunnel Segment portion of the tunnel terminates at Shaft E. The eastern reach terminates at the "WYE" where it meets the East Tunnel Segment. Shafts NE and NW will be constructed on the northwest side of Norumbega Reservoir where surface work will include construction of valve chambers and surface piping to allow connections to the Hultman Aqueduct and Norumbega Reservoir. The design at Shaft N includes provisions for future connections to the Norumbega Covered Storage Facility and the proposed Metropolitan Tunnel Loop. Construction: Shaft 5A was excavated near the intersection of Route 128 and the Massachusetts Shaft 5A- CP3 Turnpike. Construction: Construction of the eastern portion of the tunnel. An approximately 4,400-feet Eastern Tunnel long, 12-feet finished diameter tunnel is being constructed from the Shaft 5A Segment – CP3A bottom through the “WYE” where it meets the Middle Tunnel Segment and on to Shaft W where a shaft connection to the Loring Road storage tanks will be made. Construction: Miscellaneous surface work to be grouped under one contract. At this time, there Surface Work – is no work assigned to this contract, as all earlier items have been included in other CP4 contracts. Construction: Massachusetts Highway Department (MHD) salt storage operations were relocated MHD Salt Sheds – from the Shaft 5A site to a new, nearby location on MHD property on Recreation CP5 Road in Weston. This allowed demolition of the MHD salt sheds at the Shaft 5A site. Construction: Full inspection and partial rehabilitation of the Hultman Aqueduct along with Hultman construction of interconnections from the MetroWest Tunnel to the Hultman Interconnection/ Aqueduct at Shafts L, 5A, N, and E, and the connection between Norumbega Inspection/ Covered Storage and the Hultman. Rehabilitation – CP6 Transmission 102 Construction: Pressure testing of the MWWST from Shaft E (west) to Shaft W and 5A, and Testing and disinfection and dechlorination of the entire tunnel from Shaft D to Shafts W and Disinfection – CP7 5A, and final disinfection of Norumbega Covered Storage tanks. Also includes the disinfection and dechlorination of the Wachusett Aqueduct and the piping connections through Walnut Hill to MetroWest Shaft D. Construction: Construction of surface facilities at the Shaft W site including a 20 million-gallon Loring Road storage facility that replaces the function of the existing Weston Aqueduct/Weston Covered Storage- Reservoir system, allowing the system to be taken off-line and placed on CP8 emergency stand-by status. The storage facility has been constructed as two concrete tanks partially buried in a hillside adjacent to Shaft W. Connections will be made under this contract at Shaft W to two WASM (1 and 2) low service mains and the WASM 4 high service main, as well as to the 7-feet diameter branch of the Hultman Aqueduct. Also includes rehabilitation of 4,100 linear feet of 60-inch pipe and four master meters. Construction Full inspection of all construction activity, as well as provision of construction Management/ support services including environmental and safety compliance, claims assistance, Resident contract administration, quality assurance